1. Field of the Invention
This invention relates to a pattern defect inspection apparatus for detecting defects and foreign matters of a circuit pattern on a sample.
2. Description of the Related Art
Foreign matters and defects (short-circuit, wire breakage, etc) on a semiconductor wafer, if any, will result in insulation defects and short-circuits of wires and capacitors and film breakage of gate oxide films and eventually, in the defects of semiconductor devices in semiconductor production processes.
Structures of semiconductor devices have got more and more diversified and complicated in recent years. Semiconductor devices are classified into memory products that are constituted mainly of repetition patterns and logic products that are constituted mainly of non-repetition patterns, for example. Since product life of the semiconductor device products is relatively short, the production yield must be improved within a short period. It has thus become more important to reliably find out so-called “target defects” that must be managed during fabrication of the semiconductor devices.
The “target defect” includes voids and scratches in a CMP process in addition to foreign matters and pattern defects in a production process of each of film formation, etching and photolithography. The target defect includes further short-circuit and bridge in gate wiring and metal wiring portions such as aluminum and non-conduction and non-opening of contact apertures that connect wires.
SEM (Scanning Electron Microscope) inspection technology and optical inspection technology are generally known as technology for detecting the target defects on the semiconductor wafer described above. The optical inspection technology is divided into bright visual field inspection technology and dark visual field inspection technology. The bright visual field inspection technology illuminates a wafer through an objective lens and condenses reflected and diffracted rays of light by a condenser lens. The rays of light so diffracted are subjected to photoelectric conversion by detectors and defects are detected by signal processing. On the other hand, the dark visual field inspection technology illuminates a wafer from outside NA (Numerical Aperture) of an objective lens and condenses scattered rays of light by an objective lens. The rays of light so condensed are subjected to signal processing to detect defects in the same way as in the bright visual field inspection technology.
As one of the optical type dark visual field inspection technologies, JP-A-62-89336, for example, describes a detection method that makes it possible to detect foreign matters and defects with high sensitivity and high reliability by irradiating a laser beam onto a wafer, detecting scattered rays of light from the foreign matters and comparing the result with an inspection result of the same kind of wafer inspected immediately before to eliminate false information due to patterns.
As the technology for inspecting the foreign matters described above, JP-A-1-117024, JP-A-4-152545 and JP-A-5-218163, for example, describe a detection method that irradiates coherent light to a wafer, removes the rays of light generated from repetition patterns on the wafer by using a spatial filter, and stresses and detects those foreign matters and defects which do not have repetition characteristics.
A method for detecting minute foreign matters by irradiating light to the same point from multiple directions and detecting scattered rays of light at mutually different angles is known, too (JP-A-11-258157, for example).